720 



maiient teeth, but since these woiilfl with tlie Marsupials liave also 

 been incorporated in tlie tbrniation of the molars, the free teethband 

 border lingually of the Marsupialian molars could only have the 

 meaning of still a fourth series of teetii. In tiiis way the idea of 

 a series of post-permanent teeth was introduced into odontological 

 literature. 



Thus we see that oidy on account of (lie signiticance assigned to 

 the free teethband border the conceptions of prelacteal and post 

 permanent teeth were successively introduced into odontology and 

 that besides the identitlcalion of Didelpliian and Monodeiphian mam- 

 mals became different from tiiat given ity tlie older anatomists. Not 

 to mention more substantial objections which will be presently 

 explained, the general question is justified whether it was admissible 

 to build up such a far-reaching theory on such a feeble base and 

 to make morphological deductions of paramount importance from 

 such a weak starting-point to the reality of which objections might 

 moreover be raised. And if no other arguments had led me to 

 reject Kükenthal's theory as erroneous, it would already have 

 appeared to me little plausible by its general internal weakness. 



Still this theory has found several adherents. because no argunaeni 

 could be adduced by which it could a priori be declared to be false; 

 besides the theory seemingly linked the phenomena of tooth-changing 

 in Reptiles and Monodeiphian mammals. One of the characteristics 

 of the reptilian dentition is so-called polyphyodontism ; during life 

 the process of tooth-changing is an unlimited one and a number of 

 dental series evolve in succession. With mammals on the other 

 hand tooth-changing occurs only once, they only develop two dental 

 series, are diphyodontic. Exceptionally also monophyodontisra is 

 found, no toolh-cliange taking pla'je. The indeed obvious view was 

 now generally held that the diphyodontism of Mammals had developed 

 out of the polyphyodontism of Reptiles, the number of tooth-changes 

 having gradually diminished to one and hence that of the dental 

 series to two. And on account of this view the idea that with 

 Marsupials indications of four dental series would be found, namely 

 a prelacteal, lacteal, permanent and postpermanent one, had nothing 

 objectionable. On the contrary this interpretation of phenomena 

 supported the apparently so logical deduction of diphyodontism from 

 polyphyodontism. So factors were certainly present which secured 

 a favourable reception for Kükenthal's theory. 



Considerations of a moie general kind would, as was stated above, 

 have already luade this theory less acceptable for me. But my 

 object in this paper is not to point out the weak side of this theory 



